fix: pin goimports to v0.42.0 to support Go 1.24

[afrittoli]

Summary

• golang.org/x/tools@latest resolved to v0.43.0 which requires Go >= 1.25
• The module declares go 1.24.0 in go.mod, so CI fails with GOTOOLCHAIN=local
• Pins goimports to v0.42.0, the last release compatible with Go 1.24

Test plan

• CI make fmt step passes without the go >= 1.25.0 error

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.12%. Comparing base (a54a820) to head (31cd481).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #127   +/-   ##
=======================================
  Coverage   85.12%   85.12%           
=======================================
  Files         149      149           
  Lines       13095    13095           
=======================================
  Hits        11147    11147           
  Misses       1631     1631           
  Partials      317      317           

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